Commercially available flashlights marketed today employ various battery technologies that can be broadly classified as rechargeable and non-rechargeable. Examples of non-rechargeable battery technologies include cells based on alkaline, lithium, zinc-carbon, and zinc chloride. Examples of rechargeable battery technologies include cells based on lead acid, lithium ion, lithium sulfur, lithium titanate, nickel cadmium, nickel iron, nickel hydrogen, nickel metal hydride, nickel zinc, and polysulfide bromide. Rechargeable battery technologies are generally more environmentally friendly than non-rechargeable battery technologies, as once drained non-rechargeable batteries add to land fill waste and can potentially contaminate soil and water supplies.
Flashlights sold today with non-rechargeable batteries can be outfitted with rechargeable batteries by the user. For example a user may purchase a flashlight with an alkaline based battery technology and replace the batteries with rechargeable battery cells made of nickel metal hydride. Furthermore some manufacturers have offered flashlights bundled with rechargeable batteries.
However, in order to recharge such rechargeable batteries, the users must remove the batteries from the flashlight and set the batteries in a separate charging apparatus. This can be cumbersome and time consuming, and leaves the flashlight inoperable until the batteries are replaced and the flashlight is reassembled.
Manufacturers have therefore recognized a need for recharging flashlight batteries without removing the batteries from a flashlight. For example, manufacturers have designed flashlights that are sold with a base station that can recharge a flashlight when the flashlight is simply deposited in the base station, and without requiring removal of the batteries from the flashlight. Such flashlights are therefore readily usable, even during a charging phase, by simply lifting the flashlight out of the base station and turning the flashlight on.
Many such base stations recharge the battery pack using metallic conductive contact points between the base station, which is plugged into an AC circuit, and the flashlight. Other manufacturers of rechargeable flashlights use inductive charging stations. Inductive charging uses electromagnetic induction, whereby a charger induces a current inside the flashlight which transfers electric power to the batteries. An induction coil in the charger (primary coil) creates an alternating electromagnetic field, and a second induction coil (secondary coil) in the flashlight takes power from the electromagnetic field and converts it back to electrical current to charge the batteries. Essentially two induction coils in close proximity combine to form an electrical transformer.
One example of inductive charging is described in U.S. Pat. No. 3,938,018 to Dahl, where “[a] normal 117-volt, 60 cycle source is converted into a high frequency signal resulting in radiation of a substantial portion of the energy in the signal. A receiving coil is inductively coupled to the radiation over a given distance substantially less than a wave length of the high frequency signal to provide a received signal without the necessity of any electrical wires. The received signal in turn is converted into a D.C. signal and passed to a rechargeable battery for charging. The inductive coupling can be utilized for recharging portable electrical instruments having rechargeable batteries or for charging larger rechargeable batteries such as used in electrically driven vehicles.” Thus a flashlight outfitted with such technology does not require external electrical contacts between a base station and the flashlight.
However, commercially available rechargeable flashlights that include a recharging base station are generally more expensive than comparable non-rechargeable flashlights. For example, the Maglite® (a registered trademark of Mag Instrument, Inc.) brand rechargeable flashlights manufactured by Mag Instrument, Inc. generally retail at significantly higher prices than the Maglite® brand non-rechargeable flashlights.
There is therefore a need for an improved method of converting a non-rechargeable flashlight to a rechargeable flashlight.